FIG. 3 is a diagrammatic longitudinal sectional view of a high pressure pump for an accumulator fuel injection system.
A high pressure pump 100 is connected to an engine (not shown) via a coupling 12 that is connected to a flywheel 11 connected to a camshaft 3 of the pump 100 to be driven by the engine.
The same number of cams 2 as that of cylinders of the engine is formed on the camshaft 3. Each cam 2 allows each plunger 1 to be reciprocated via each tappet 4 as the camshaft 3 rotates. Fuel pressurized to a high pressure by the plungers 1 is accumulated in an accumulator not shown in the drawing.
An electromagnetic valve 5 is provided above each of plunger rooms 1a of the high pressure pump 100. The electromagnetic valves 5 are connected via wiring 7 to a controller (ECU) 6 so that its closing-and-opening is controlled to control fuel supply to the accumulator and shutoff thereof.
To the controller (ECU) 6 is sent a detection signal of rotation position of the cam 2 from a cam top position detector 9 via wiring 8. A cam top position pointer 11a is attached on the circumference of the flywheel 11 at a position corresponding to the top of a cam lobe 21 of a far left cam 2, and a rotation position of the camshaft 3 when the cam top position detector 9 has detected the cam top position pointer 11a is determined as a reference cam top position.
A distribution type fuel pump is disclosed in patent literature 1 (Japanese Laid-Open patent Application No. 59-192842). According to the literature, rotation position of a rotation shaft is detected by a position detector by detecting a plurality of cam top position pointers attached to the circumference of the rotation shaft.
In the conventional high pressure pump for the accumulator fuel injection system as shown in FIG. 3, the detection signal of the cam top position pointer 11a detected by the cam top position detector 9 once per one rotation of the camshaft 3 is imputed to the controller (ECU) 6.
Discharge amount of fuel is controlled by controlling closing-and-opening of the electromagnetic valve 5. Discharge from the plunger room 1a begins and ends respectively when the electromagnetic valve 5 closes and opens the inlet port to the plunger room la. In order to control the timing of closing-and-opening of the electromagnetic valve 5, it is necessary to detect the reference cam top position. In the case of FIG. 3, the reference cam top position is detected once per one rotation of the camshaft 3. In an accumulator fuel injection system, fuel pressurized to a high pressure is accumulated in an accumulator and then injected from an injector according to electric signals sent to the injector, so there has been a problem that more time is required from the start of engine staring operation to the start of the engine as compared with a case of a conventional jerk fuel injection pump. As the discharge of fuel from the plunger room 1a to the accumulator is controlled by controlling closing-and-opening of the electromagnetic valve 5, rotation position of the cam top must be detected. However, since the rotation position of the reference cam top is detected once per one rotation of the camshaft, the time required to start the engine may further increase because the rotation speed of the camshaft is very slow at engine starting.